The inventive concepts generally relate to semiconductor memory devices, and more particularly, the inventive concepts relate to semiconductor memory devices which stores memory characteristic information, to memory modules and memory systems including the same, and to methods of operation the same.
A Dynamic Random Access Memory (DRAM) is an example of a semiconductor memory device having a finite data retention characteristic. That is, even for a non-defective memory cell, the validity of data stored in the memory cell is not guaranteed after the lapse of a specified time period. As such, refresh functionality is adopted in which the DRAM refreshes (rewrites) data stored in the memory cell at the expiration of each refresh period. The refresh period is set as a specification value of the DRAM.
Refresh periods may be reduced (i.e., refresh frequency may be increased) as device integration is increased. This is because, for example, the size (capacitance) of memory cell capacitors can decrease, and the adverse effects of parasitic capacitances and the like can increase, as the DRAM becomes more highly integrated.
In the meantime, a weak cell (i.e., a cell with an unacceptably low data retention characteristic) may be replaced with a redundancy cell of the semiconductor memory device. However, the efficiency of this approach is limited since the redundancy cell may have the same or similar memory characteristics as the so-called weak cell, particularly as device integration is increased. It may thus be necessary to devote considerable resources to the provision of redundancy cells.